Flying heads are employed, for example, in magnetic disk lot drives wherein a magnetic head is mounted on a slider which flies at a small distance over a moving magnetic disk. The magnetic head records and reads data in concentric data tracks on the surface of the moving magnetic disk.
Key elements in improving the performance of magnetic disk drives are the capacity of data stored on the magnetic disk and the speed of accessing that data. By decreasing the flying height, a smaller magnetic recording signal may be effectively read by the magnetic head, allowing the linear recording density of a track to be increased, thereby increasing the data capacity of each track. The speed of accessing data is often increased by increasing the rotational velocity of the disk. A corresponding increase in the ambient temperature of the disk drive is likely to occur, thereby affecting the temperature of the head and slider.
Typically, a flying head slider is made of a ceramic material (e.g., Al.sub.2 O.sub.3 TiC) and the suspension to which the slider is attached is made of a spring steel, which materials have different linear thermal expansion coefficients. This mismatch in thermal expansion coefficients results in stress between the spring steel suspension and the attached ceramic slider. This stress causes the slider to bend, resulting in a distortion of the ceramic slider as well as its air bearing, which is the surface of the slider facing the moving magnetic disk and is the surface which controls the flying characteristics of the slider. Consequently, the constancy of the flying height or the flying angle of the slider with respect to the disk may be adversely affected. Specifically, if the flying height increases, or if the flying angle moves the magnetic head further from the disk, the read signal amplitude will decrease considerably. Similarly, if the flying height decreases, or if the flying angle moves the magnetic head closer to the disk, the risk of the head contacting the disk (head crash) is increased.
This problem is noted in U.S. Pat. No. 5,636,088, Yamamoto et al., issued Jun. 3, 1997, and sets the ratio of the flexure spring to the height of a slider to a ratio of 0.047 or less, sets the ratio of the height of the slider to the length of the slider to a ratio of 0.245 or less, or sets the ratio of an actual adhesion area of the slider to the possible adhesion area to a ratio of 0.42 or less, while adding a temperature compensation member adhered to the slider or the flexure spring.
However, reduction in the thickness of the suspension, or reduction in the thickness of the slider, have the potential to produce instability in the slider/suspension assembly with corresponding instability in the slider-disk flying characteristics.
Some adhesives have low glass transition temperatures. If the operating temperature is greater than the glass transition temperature (T.sub.g) of the adhesive, the adhesive will generate much less stress and the slider will bend much less. However, for these low Tg adhesives, the "creep" property is usually worse. "Creep" is the spreading of microscopic cracks from bonding imperfections, which is worse under higher temperature and stressed conditions, such that the strength of the adhesive is reduced after a period of time. Thus, upon receiving a shock, the slider might sheer off the suspension. Additionally, other considerations may make it desireable to operate the drive at a temperature lower than the glass transition temperature.